two separate PV arrays - should I use one or two controllers?

petefink
petefink Registered Users Posts: 6 ✭
in Solar Beginners Corner #1
just starting design but have been getting conflicting advice. plant to have one 2 x2 PV array (100 watt 12 V panels) at an adjustable tilt from 0 deg to 70deg and another 1 x2 array (same panels) at a fixed 12 deg from horizontal. Arrays are separated by about 30 feet but both are same southern orientation. Plan to have three 1x2 series strings for nominal 24 V each (two strings on the tiltable array and one string on the fixed array). Plan to use one 12 or 24 v battery bank. Should I use one (larger) MPPT controller for both arrays or two (smaller) MPPT controllers - one for the 1x4 tiltable and one for the 1x2 fixed? Or doesn't it make much difference (in which case I'll go with cheapest alternative). Thank you. Peter
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: two separate PV arrays - should I use one or two controllers?

    Welcome to the forum Peter.

    So on the tilting mount you will have four 100 Watt panels configured as two parallel strings of two in series. On the fixed mount you will have two 100 Watt panels configured as one string of two in series.

    There is no reason you can not parallel all three strings to one charge controller. It should be capable of >20 Amps @ 24 Volts or >40 Amps @ 12 Volts. If I were you I'd go with the 24 Volt system; it's more efficient and one MidNite Kid would handle the job for about $300.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #3
    Re: two separate PV arrays - should I use one or two controllers?

    If you are using Vmp-array ~ 35-38 volts on a PWM controller and a 24 volt battery bank--There is no reason to use separate charge controllers.

    If you are using Vmp-array ~35-38 volts (or higher) on a 12 volt battery bank, then you need to use an MPPT charge controller...

    Basically you want Vmp-array~18 volts for charging a 12 volt battery bank or Vmp-array~36 volts to charge a 24 volt battery bank with a PWM controller.

    If you are using an MPPT type charge controller (which can take higher voltage/lower current and efficiently down convert to low voltage/high current used to charge the battery bank), the recommendation is to use one MPPT controller for each "plane" of solar array. The MPPT controller "tracks" the Vmp-array voltage and with two arrays mounted different orientations (or one tracking as in your case), their temperatures will be different and cause a loss of voltage tracking and efficiency (two arrays with different Vmp-array voltage, there is no "one perfect" voltage).

    Personally, if costs are important (and they usually are), I would try one MPPT controller on the two arrays and see how it performs. It won't hurt anything.

    Also, I moved your post to the "Beginners Forum" (not the Announcement Forum).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • petefink
    petefink Registered Users Posts: 6 ✭
    #4
    Re: two separate PV arrays - should I use one or two controllers?

    thanks for the advice and the move, peter
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  • petefink
    petefink Registered Users Posts: 6 ✭
    #5
    Re: two separate PV arrays - should I use one or two controllers?

    thanks for the help, peter
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